This invention relates to a 2-metal layer TAB tape and a both-sided CSP.BGA tape, and a process of producing them.
1. Background Art
Various types of wiring boards having a conductor layer on both sides thereof are in use. Such wiring boards include those using a flexible substrate, e.g., polyimide, such as a TAB (tape automated bonding) tape, a CSP (chip size package), a BGA (ball grid array), and an FPC (flexible printed circuit); and so-called multilayer printed wiring boards using a rigid substrate, e.g., a glass epoxy laminate.
A substrate having a conductor layer on both sides thereof is produced by making sprocket holes along the both width direction edges of a substrate in the longitudinal direction at regular pitches by a punching press. Sometimes through-holes, etc. are also made by this punching press.
Thereafter a wiring layer is formed on both sides of the substrate by etching and the like. Through-holes are then made in the substrate by means of a punching machine. The through-holes are filled with a conductor by a punching (implanting) process, followed by forming a finish plating layer.
In forming the wiring layer by an etching process, the tape is transported by employing the sprocket holes. The sprocket holes are also available as the pilot holes for registration in filling the through-holes with a conductor (implanting process).
However, there are some cases that slight deformation of the sprocket holes takes place during a wiring layer formation process. By using the deformed sprocket holes as the registration hole for the implanting process, the registration accuracy becomes worse. Further, since the sprocket holes are rectangular, a slight shift occurs when the deformed sprocket holes are used as pilot holes, which also results in that the registration accuracy becomes worse in the implanting process. The inaccuracy of registration has given rise to the fluctuation of the properties of products by lot-by-lot manufacturing when they are transferred to a mass production stage.
2. Disclosure of the Invention
Accordingly, an object of the present invention is to provide 2-metal layer TAB and both-sided CSP.BGA tapes and to provide a process of producing the tapes which do not have any fluctuation of the properties of products, even when they are produced in a mass production system.
As a result of investigation, the present inventors have found that the above object is accomplished by making round holes between sprocket holes which are used as pilot holes in filling through-holes with a conductor by means of a punching press.
The present invention has been completed based on the above finding. The present invention provides a 2-metal layer TAB or both-sided CSP.BGA tape having an insulating substrate and a wiring layer provided on at least both sides of the substrate, the substrate having evenly spaced sprocket holes on both width direction edges in the longitudinal direction thereof and also having through-holes formed with a punching press, and the through-holes being filled with a conductor by means of a punching press such that the conductor and the wiring layers are electrically connected, which is characterized by having round pilot holes between the sprocket holes formed in the longitudinal direction thereof.
The present invention also provides a process of producing a 2-metal layer TAB or both-sided CSP.BGA tape which comprises forming sprocket holes and round pilot holes along both width direction edges of an insulating substrate in the longitudinal direction thereof alternately and at regular pitches by a punching press, forming a wiring layer or a metal foil on at least both sides of the substrate, forming through-holes with a punching press, and filling the through-holes with a conductor with a punching press to electrically connect the conductor to the wiring layers or the metal foils.